Single cylinder truck-mounted brake systems for rail cars have been in use for some time with varying degrees of success. One such system is shown in U.S. Pat. No. 3,780,837 issued to Haydu.
While such prior art devices have achieved a measure of success, various problems and drawbacks have been noted. The brake beams of these systems are usually heavy section castings which include integral means for mounting brake shoes, brake cylinders, parking brake linkages and related equipment. The large size of these beams is made necessary by the location on the beams of the points at which the braking force is applied to the beams by the brake cylinder. Usually, the pivot points for the linkages interconnecting the parallel beams and the brake cylinder are located well inboard of the location at which braking force is transferred from the beam to the rail car wheels. This results in the generation of high bending moment stresses in the beams, which must be absorbed by heavy crossections. Clearly, the large beam size results in increased component weight and cost, plus reduced operating efficiency. Moreover, the use of integral brake heads requires beam removal should the brake heads become worn due to wear of the brake shoes.
Prior art systems have also been criticized because of the rather large amount of pressurized fluid required to stroke their long stroke actuators, especially those actuators having no provision for slack adjustment. Provision of long stroke capability is desirable to permit the use of thicker, longer lasting brake shoes. Where slack adjustment is provided, it frequently adjusts only for increases in brake shoe clearance due to wear but not for decreases due to shoe or wheel replacement.
Another drawback of prior art systems of this type has concerned the manual or parking brake system. Frequently, as in older parallel beam systems, the parking brakes are applied through a linkage mounted on one side of the truck, to provide clearance with the central portions of the truck and bolster. Due to the off-center mounting of the parking brake linkage, the brakes tend to be applied first on the side nearer the linkage mount and then, if at all, on the side further from the linkage mount. Due to the point of force application, high stresses are induced in the beams, which must be of a heavy crossection. The off-center mounting may result in application of insufficient braking force in cases where contact is made only on one side. Furthermore, crewmen checking a car to ensure parking brake application may mistakenly conclude that the brake has not been applied after looking at the shoes and wheels on the side opposite the linkage mount.